In recent years, health hazards and industrial accidents caused by mental fatigue due to overwork have become a social problem.
A flicker test is a known method of measuring mental fatigue. The test relies on human inability to perceive a light pulse, i.e., a flicker, when the light source is blinking at high speeds; however, as the speed (frequency) decreases, perception becomes possible when the frequency is dropped to a certain value. The frequency at which the human perceives the flicker is called a flicker perception threshold, which is known to vary depending on mental fatigue. More specifically, the flicker perception threshold decreases as fatigue becomes more intense; that is, a person cannot perceive a flicker at high frequency when mental fatigue is intense, and perception finally becomes possible when the frequency is dropped to a smaller value than that of a frequency of a flicker that is perceivable by a person in a healthy condition. Using this phenomenon, various flicker test methods and systems were suggested.
For example, Patent Literature 1 discloses a massage device that uses a portable terminal such as a PDA to measure a flicker value before and after a massage, and determines whether the degree of fatigue is improved by the massage.
Patent Literature 2 discloses a system in which a host computer remotely controls a computer terminal in front of the test subject via a network, so as to present some kind of stimulation to the test subject, control the stimulation, and record the reaction of the test subject, thereby measuring the functioning eyesight (actual eyesight) of eyes of the test subject under stress. The document also discloses a method of measurement of flicker perception eyesight to determine the ability to perceive a flicker, as an example of eyesight measurement.
Patent Literature 3 discloses a system comprising a blinking light emitting display device and a computer terminal. The blinking light emitting display device presents flicker stimulation under the control of a computer terminal via a communication cable, and the computer terminal records push-button operations involved in a flicker perception. The measurement data is compared with other data previously stored so as to measure the degree of fatigue.
Although Patent Literature 4 is not intended to measure a flicker value, it discloses a stress control system in which biological data is obtained from a sensor that is attached to a cell phone so as to be in contact with a user; based on the obtained data, the stress state is recognized with reference to psychophysiological parameters. Then, an inference engine is allowed to select an image, which can improve the stress state, and the selected image is displayed on the display screen of the cell phone.